Radio receiver using level-variable reference, signal for discriminative detection of data signal and signal discrimination method

ABSTRACT

A radio receiver apparatus for receiving a spread spectrum signal in which a signal derived through a level detection of a signal demodulated by a correlative demodulator and a signal obtained by extracting a signal component of a synchronous frequency from a reception synchronizing clock are combined to thereby generate a reference signal having a level which changes in accordance with change of the detected signal, and by comparing the detected signal with the reference signal, the received signal is discriminated.

BACKGROUND OF THE INVENTION

The present invention relates to a receiver apparatus or equipment for aradio transmission system. More specifically, the present invention isconcerned with a radio receiver apparatus for receiving discriminativelyintrinsic data or information signals which are transmitted throughradio communication between or among office automation apparatuses ormachines.

Heretofore, for transfer or communication of information or data among aplurality of office automation (OA) machines, there has been adopted amethod of interconnecting the machines to one another through the mediumof cables. However, for interconnecting a large number of such machinesby cables, troublesome and expensive wiring works are required, whichprovides difficulty to rearrangement or alteration of the machines uponrenewal of office layout as well as installation of additional machines.For solving such problems, there is conceivable a radio or wirelessinterconnection or communication among the machines by making use ofelectromagnetic wave or radio channels. However, such wirelesscommunication facilities are not adopted widely because of problems suchas limitation imposed to the radio output power as well as carrierfrequency, interference with other machines and so forth.

On the other hand, as a communication system designed for specificapplication, there has been developed a so-called spread spectrumcommunication system according to which data or information signal isspread over a wide frequency band so as to allow the signal to betransmitted with electromagnetic wave of low power density. This systemor scheme is advantageous in that disturbance to the other machines canbe suppressed to a minimum and that the system is less susceptible tointerference of the other machines because of spreading and demodulationbased on a pseudo noise coding or sequentialization. In the spreadspectrum communication system, there is adopted a spreading code orsequence generally known as PN code or sequence for modulating theinformation or data signal over a wide band. However, in thetransmitter/receiver system in which the spread spectrum scheme isadopted, the correlative demodulation circuit for demodulating thesignal spread by using the PN code or sequence is extremely complicatedin respect to the circuit configuration. Under the circumstances,several demodulating schemes have been proposed. Among them, there maybe mentioned a scheme or method of employing a SAW (Surface AcousticWave) matched filter for the correlative demodulation or detection, as amethod capable of demodulating the signal with high reproducibility witha simple circuit configuration, as is disclosed in JP-A-5-327661.

The scheme for reproducing data by detecting correlated data with adelay by using the SAW matched filter as the correlator is certainlyadvantageous in that the time taken for establishing synchronization canbe shortened and that the circuit structure can be simplified withoutneed for PN generating circuit, synchronizing circuit and the like forthe demodulation. However, because of the radio communication, theoutput level after the detection may change finely at random, givingrise to a problem that identification error due to deterioration of theS/N ratio is likely to take place even when the signal level inputted tothe demodulator is stabilized by resorting to the AGC (Automatic GainControl) technique.

SUMMARY OF THE INVENTION

In the light of the state of the art described above, it is an object ofthe present invention to provide an improved structure of the radioreceiving apparatus which can ensure improvement of S/N ratio of thedemodulated signal by taking advantage of the characteristics of the SAWmatched filter mentioned above.

In view of the above and other objects which will become apparent as thedescription proceeds, there is provided according to a first generalaspect of the invention a first scheme according to which thedemodulated output of the SAW matched filter is subjected to a leveldetection to be thereby used as a reference signal for discriminativeidentification of the received signal with a delay after detectionthereof.

Further provided according to a second general aspect of the inventionis a scheme for generating a signal synchronized with a burst-likedemodulated signal of the SAW matched filter from a data synchronizingpulse signal derived from the correlative demodulation, whereon theaforementioned signal is superposed onto the reference signal generatedaccording to the first scheme mentioned above.

By detecting the level of the demodulated signal outputted from the SAWmatched filter and using it as the reference signal for a comparatorwhich is provided for the signal discrimination after the detection witha delay, it is possible to change or vary the reference signal employedfor the discriminative identification of the signal by following minuteor fine change of detection output level due to variation of thereceived signal level, whereby S/N ratio can be protected againstdeterioration or degradation due to the level variation.

Furthermore, by generating the signal synchronizing with the burst-likedemodulated signal of the SAW matched filter from the synchronizingpulse of the data generated through the correlative demodulation andsuperposing the synchronous signal onto the reference signal mentionedabove, the S/N ratio can significantly be improved by broadening thedynamic range with the reference signal being set to a low level at thetime point or timing for the signal discrimination or identification,while the level of the reference signal is increased during the otherperiod, to thereby suppress erroneous operation due to noise to apossible minimum.

Thus, according to the teachings of the present invention, theburst-like signal can discriminatively be identified or detectedreliably and stably with a simple structure in a system where the signallevel varies constantly such as the radio communication system, wherebya radio receiving apparatus ensuring an improvement of the S/N ratio ofthe received signal.

The above and other objects, features and attendant advantages of thepresent invention will more easily be understood by reading thefollowing description of the preferred embodiments thereof taken, onlyby way of example, in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the description which follows, reference is made to thedrawings, in which:

FIG. 1 is block diagram showing a structure of a radio receiveraccording to an embodiment of the present invention;

FIG. 2 is a circuit diagram showing in concrete an exemplary circuitconfiguration of the radio receiver shown in FIG. 1;

FIG. 3A is a waveform diagram showing a waveform in a signaldiscriminating part of the receiver shown in FIG. 1;

FIG. 3B is a waveform diagram showing a data signal for transmission;

FIG. 3C is a waveform diagram showing a waveform of the data signal fortransmission after modulation with a PN code or sequence;

FIG. 3D is a waveform diagram showing a waveform of a signal inputted toa comparator shown in FIG. 2;

FIGS. 3E, 3F and 3G are waveform diagrams showing signal waveformsmaking appearance at terminals (23, 24 and 25) of the receiver shown inFIG. 2;

FIG. 4 is a block diagram showing a structure of a radio receiveraccording to another embodiment of the present invention;

FIG. 5 is a circuit diagram showing in concrete an exemplary circuitconfiguration of the receiver shown in FIG. 4;

FIGS. 6A, 6B and 6C are waveform diagrams illustrating input and outputsignals of comparators shown in FIG. 5;

FIG. 7A shows, by way of example, conventional signal discrimination;

FIG. 7B shows an exemplary signal discrimination realized with thereceiver implemented in the configuration shown in FIG. 5;

FIG. 8 is a block diagram showing a structure of a radio receiverapparatus according to another embodiment of the present invention; and

FIGS. 9A and 9B show waveform diagrams for illustrating a relationbetween a detection output waveform and a reference signals in thereceiver shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described in detail in conjunctionwith what is presently considered as preferred or typical embodimentsthereof by reference to the drawings. In the following description, likereference characters designate like or corresponding parts throughoutthe several views.

FIG. 1 is block diagram showing a structure of a radio receiveraccording to an embodiment of the present invention. In the figure,reference numeral 1 denotes a correlative demodulation part, 2 denotes adelaying/detecting part, 3 denotes a positive polarity comparing part, 4denotes a negative polarity comparing part, 5 denotes a datademodulating part, 6 denotes a synchronizing pulse generating part, 7denotes a level detecting part, 8 denotes a polarity inverting part, 9denotes a received signal input part and a reference numeral 10 denotesa demodulated data output part.

In the case of the receiver according to the instant embodiment of theinvention, it is presumed that data transmitted and received hasundergone a DPSK (Differentially Encoded Phase Shift Keying) modulationand then a spreading modulation by using a high-speed clock signal,whereby a spectrum spread signal is derived to be sent out from thetransmitter. In the receiver, this signal is caught by an antenna andinputted to the correlative demodulating part 1 by way of the receivedsignal input part 9 after having been amplified to a prescribed level.The correlative demodulating part 1 matches the received signal with apreset spread code or sequence. When coincidence results from thematching, the correlative demodulating part 1 outputs a burst-likedemodulated signal which is then inputted to the delaying/detecting part2. Because of the DPSK modulation performed on the side of thetransmitter, there are outputted from the delaying/ detecting part 2burst-like detection signals of positive and negative polarities,respectively, in dependence on the phase of the demodulated output,which signals are then inputted to the positive polarity comparing part3 and the negative polarity comparing part 4, respectively. Furthermore,the burst-like demodulated signal outputted from the correlativedemodulating part 1 undergoes level detection in the level detectingpart 7. The output of the level detecting part 7 is directly inputted tothe positive polarity comparing part 3 as a reference voltage and at thesame time to the negative polarity comparing part 4 as a referencevoltage after having been inverted by the polarity inverting part 8. Thepositive polarity comparing part 3 and the negative polarity comparingpart 4 determine the polarity of the output of the delaying/detectingpart 2, the results of which are then supplied to the data demodulatingpart 5 and the synchronizing pulse generating part 6, respectively. Thedata demodulating part 5 demodulates the data derived from the outputsof the positive polarity comparing part 3 and the negative polaritycomparing part 4, respectively. The demodulated data are then set outfrom the demodulated data output part 10 in the timing determined by adata clock signal generated by the synchronizing pulse generating part6. Owing to the level detection of the burst-like demodulation output ofthe correlative demodulating part 1 by the level detecting part 7 tothereby obtain the comparison reference voltages for the polaritycomparing parts 3 and 4, respectively, the reference voltages for thepolarity comparing parts 3 and 4 change as the detection level outputtedfrom the delaying/detecting part 2 varies in following variation in thelevel of the received signal. Thus, there can be realized a stable datademodulation notwithstanding of variation of the received signal levelwhich is brought about by changes in the radio transmission environment.

In the case of the illustrated embodiment, the output of the correlativedemodulating part 1 is inputted to the level detecting part 7. It shouldhowever be noted that similar effects can equally be obtained by thelevel detection of the output of the delaying detecting part. Further,although not illustrated in detail, a part of the output of the leveldetecting part 7 is fed back to a gain control/amplifier part providedat a stage preceding to the received signal input part 9 so that thesignal level inputted to the input part 9 is controlled to be constantnotwithstanding of change of the reception level. Since the signal asinputted contains a signal component corresponding to the data and noisecomponents, change of level of noise is reflected as a change of thelevel of the signal component.

FIG. 2 is a circuit diagram showing in concrete an exemplary circuitconfiguration of the receiver shown in FIG. 1. In FIG. 2, parts whichserve for the same functions as those described above by reference toFIG. 1 are denoted by like reference numerals, and repeated descriptionthereof will be omitted. Referring to FIG. 2, a reference numeral 11designates a SAW (Surface Acoustic Wave) matched filter which isincorporated in or which corresponds to the correlative demodulatingpart 1 mentioned previously. Further, a numeral 12 denotes a SAW(Surface Acoustic Wave) delay line, 13 denotes a double balanced mixer(DBM), and a numeral 14 denotes an amplifier circuit, wherein the SAWdelay line 12, the double balanced mixer 13 and the amplifier circuit 14cooperate to constitute a circuitry corresponding to thedelaying/detecting part 2. Furthermore, reference numeral 15 denotes acomparator and 20 denotes an amplifier circuit, both of which correspondto the positive polarity comparing part 3. On the other hand, thenegative polarity comparing part 4 is constituted by a comparator 16.Moreover, a numeral 17 designates an OR circuit which corresponds to thesynchronizing pulse generating part 6. Additionally, a reference numeral21 designates an amplifier circuit which corresponds to the polarityinverting part 8. Finally, reference numeral 23 and 24 denote terminalsof positive and negative polarities, respectively, while a numeral 25denotes a synchronizing pulse output terminal.

In the case of the instant embodiment of the invention, a SAW matchedfilter 11 is employed as the correlative demodulator for the receivedspread signal, wherein the spread signal received from the antenna isamplified to a preset level to be subsequently inputted to the SAWmatched filter 11 from the received signal input part 9. In the SAWmatched filter 11, there has previously been provided the spread code orsequence in the form of a corresponding electrode pattern. When thespread sequence of the received signal coincides with the electrodepattern of the SAW matched filter 11, the received signal of one periodis added in phase, whereby a burst-like demodulated signal is outputtedin every period. The demodulated signal is so distributed that a partthereof is inputted intact to the double balanced mixer 13, while otherpart is inputted to the double balanced mixer 13 after having beendelayed for one period by the SAW delay line 12. Because of the DPSKmodulation performed previously on the transmitter side, there makesappearance at the output of the double balanced mixer 13 a burst-likedetection output of positive or negative polarity in dependence on thephase of the demodulated output signal. The detection output of thedouble balanced mixer 13 is applied to the inputs of the comparators 15and 16, respectively, after having been amplified by the amplifiercircuit 14.

FIG. 3A is a waveform diagram showing a waveform in the signaldiscriminating part of the receiver. Further, FIGS. 3B to 3G arewaveform diagrams illustrating exaggeratedly relations between the datafor transmission and the demodulated waveform in a temporal period "T"shown in FIG. 3A. More specifically, FIG. 3B is a waveform forillustrating the data as transmitted, FIG. 3C is a waveform diagramshowing a waveform of the data signal for transmission after modulationwith a PN code or sequence, and FIG. 3D is a waveform diagram showing awaveform of the demodulated output signal of the amplifier circuit 14.

In FIG. 3D, the time is taken along the abscissa with the amplitude ofthe output signal of the amplifier circuit 14 being taken along theordinate. As can be seen in FIG. 3D, for the voltage level V₁ during aperiod in which the modulated signal is absent, a burst-like detectionoutput "a" of positive or negative polarity is produced in every periodof the spread sequence, i.e., at every data bit of the transmittedsignal, wherein by detecting discriminatively the polarity of thisdetection output signal, it is possible to perform the datademodulation. A part of the burst-like demodulated output of the SAWmatched filter 11 is distributed to two parts after having undergonelevel detection in the level detecting part 7, wherein one part of theburst-like demodulated output of the SAW matched filter 11 is applied tothe reference signal input terminal of the comparator 15 as a thresholdvoltage after amplification in the amplifier circuit 20. The comparator15 compares the output signal of the delaying/detecting part 2 with thereference signal mentioned above to thereby extract the burst signal ofpositive polarity, which is then outputted from the positive polaritydetection output terminal 23. On the other hand, the other part of theoutput of the level detecting part 7 undergoes polarity inversion in theamplifier circuit 21 relative to the reference voltage (V₁ in FIG. 3D)to be subsequently applied to the reference signal input terminal of thecomparator 16 as a threshold voltage after amplification. In thecomparator 16, the output of the delaying/detecting part 2 is comparedwith the reference signal, whereby the burst signal of negative polarityis extracted to be outputted from the negative polarity detection outputterminal 24.

FIG. 3D is a waveform diagram sowing an output voltage "b" of theamplifier circuit 20 and an output voltage "c" of the amplifier circuit21. Further, FIGS. 3E and 3F are waveform diagrams showing signalwaveforms making appearance at the positive and negative polaritydetection output terminals 23 and 24, respectively.

Since the comparison reference signals "b" and "c" are generated by thelevel detecting part 7, the levels of these reference signals "b" and"c" change in following the change of the levels of the burst signals ofnegative and positive polarities, respectively, which are outputted fromthe amplifier circuit 14. Thus, it is possible to perform the detectionstably without deviating from the peak of the burst signalnotwithstanding of fine fluctuation of the burst signal level, as can beseen in FIG. 3A. Thus, the received data can be reconstituted orreproduced on the basis of the outputs available from the positivepolarity detection output terminal 23 and the negative polaritydetection output terminal 24. Besides, by logically summing the outputsof the comparators 15 and 16 by the OR circuit 17, a pulse signal(reception clock signal) synchronized to the burst-like demodulatedsignal as shown in FIG. 3G can be obtained to be subsequently outputtedfrom the synchronizing pulse output terminal 25.

As is apparent from the foregoing, by virtue of such arrangement taughtby the invention that the level of the burst-like demodulated output ofthe SAW matched filter 11 is detected by the level detecting part 7 tobe used as the comparison reference voltage for the comparators 15 and16 for the purpose of polarity detection, stable data demodulation canbe accomplished regardless of minute or fine fluctuation of the receivedlevel as brought about by environmental factors for the radiotransmission or communication because when the signal levels inputted tothe comparators 15 and 16 change in response to change of thedemodulated level outputted from the SAW matched filter 11 due to changeof the received signal level, then the reference voltage for thesecomparators 15 and 16 change correspondingly.

Although the SAW matched filter is employed as the correlativedemodulator in the receiver according to the instant embodiment of theinvention, similar advantageous effects can be obtained by using othertype correlative demodulator such as a SAW convolver, a digital matchedfilter or the like.

FIG. 4 is a block diagram showing a structure of a radio receiveraccording to another embodiment of the present invention. In the figure,parts serving for same or equivalent functions as those shown in FIG. 1are denoted by using same reference numerals and repeated descriptionthereof is omitted. Referring to FIG. 4, reference numeral 26 denotes aband limiting part, 27 and 28 denote signal synthesizing or combiningparts, respectively, and a numeral 29 denotes a polarity inverting part.In the following, description concerning the operation similar to thatof the receiver shown in FIG. 1 will be omitted.

Referring to FIG. 4, a part of the output of the synchronizing pulsegenerating part 6 is supplied to the band limiting part 26 which isdesigned to pass therethrough only the frequency component matched withthe period of the demodulated burst signal, whereby a sinusoidalwaveform signal of a same period as that of the demodulated burst signalis extracted. A part of the output of the band limiting part 26 issynthesized or combined with the output of the level detecting part 7 bythe signal combining part 28 after polarity inversion in the polarityinverting part 29, wherein the output of the signal synthesizing orcombining part 28 is supplied to the positive polarity comparing part 3as a reference signal for comparison. Furthermore, the other part of theoutput of the band limiting part 26 is combined with the output of thepolarity inverting part 8 by the signal combining part 27 and theninputted to the negative polarity comparing part 4 as the referencesignal. In the case of the receiver shown in FIG. 1, the output of thelevel detecting part 7 is made use of as the reference signal forcomparison for the positive polarity comparing part 3 and the negativepolarity comparing part 4. In this conjunction, it is noted that in theradio transmission, the demodulated level fluctuates from one to anotherperiod, as a result of which when the reference voltage is set at alevel close to the peak value of the burst-like detection signal,erroneous operation may possibly be brought about due to fluctuation ofthe detection output level. On the other hand, when the referencevoltage is set close to a quiescent level, there may arise a problemthat unwanted signal components originating in noise, disturbing signalsand the like except for the demodulated signal may be picked up. Incontrast, in the case of the receiver according to the instantembodiment (FIG. 4), the reference voltage is set low during a period inwhich the burst-like demodulated signal exists for thereby improving thedynamic characteristics of the receiver, while during the period inwhich the burst-like signal is absent, the reference voltage is set highfor preventing erroneous operation due to the unwanted signalcomponents, whereby the S/N ratio can be improved without need for usingany especial synchronizing circuit.

FIG. 5 is a circuit diagram showing in concrete an exemplary circuitconfiguration of the receiver according to the instant embodiment of thepresent invention shown in FIG. 4. In FIG. 5, parts serving for same orequivalent functions as those shown in FIG. 2 are denoted by likereference symbols, and correspondence relations to the blocks shown inFIG. 4 are designated by corresponding block identifying numerals. InFIG. 5, reference numerals 30 denotes a band-pass filter, 31 denotes adelay line, 32 and 33 denote amplifier circuits, respectively, andnumerals 34 and 35 denote capacitors, respectively. A part of the outputof the OR circuit 17 is inputted to the band-pass filter 30 which canpass therethrough only the demodulated clock frequency, whereby asinusoidal waveform signal of the clock frequency is selectivelyobtained from the output of the band-pass filter 30. Delay which thesinusoidal waveform signal suffers is then corrected by the delay line31 so as to have the timing matched with the demodulated burst signal.Thereafter, the output signal of the delay line 31 is amplified andcombined or synthesized with outputs of the amplifier circuits 20 and 21via the capacitors 34 and 35 after amplification by the amplifiercircuits 32 and 33, respectively, to be used as the comparison referencesignals for the amplifier circuits 15 and 16, respectively.

FIGS. 6A, 6B and 6C are waveform diagrams illustrating the input signaland the output signals of the comparators 15 and 16, respectively, inwhich time is taken along the abscissa with voltage taken along theordinate.

In the figures, a signal "a" represents the output of the amplifiercircuit 14 which is to be inputted to the comparators 15 and 16,respectively, as the detection output signal.

Further, signals "b" and "c" represent the output signals of theamplifier circuits 20 and 21 which are superposed with the outputsignals of the amplifier circuits 32 and 33 via the capacitors 34 and35, respectively. These signals are inputted to the comparators 15 and16 as the reference signals for detecting the received signal. Since theoriginal signal used for forming the signals "b" and "c" is a signalwhich is obtained by delaying signal "a" by one period of the signal "a"by the delay line 31, synchronization in phase is essentiallyestablished between the signal "a" and the signals "b" and "c".

The signal "b" is generated by amplifying the output signal of the leveldetecting part 7, while the signal "c" is derived by inverting theoutput signal of the level detecting part 7 relative to the referencevoltage V₁. To this end, the amplification factor is selectively sodetermined that error involved in the signal detection or discriminationcan be suppressed to minimum while ensuring a maximum S/N ratio bytaking into consideration various values relating to electric fieldintensity for reception as well as noise environment.

The burst signal is detected at predetermined signal positions which aredetermined on the basis of a predetermined period corresponding to thetransmitted data. In this conjunction, it is noted that when theburst-like signal "a" is positive at a predetermined signal position,i.e., when it is outputted as the burst-like signal of positive polarityrelative to the reference voltage V₁, the level of the reference signal"b" is low, while when the burst-like signal "a" is negative at apredetermined position, i.e., when it is outputted as the burst-likesignal of negative polarity relative to the reference voltage V₁, thereference signal "c" assumes a high level, as can be seen from FIG. 6A.

Further, each of the signals "b" and "c" is a sinusoidal wave having asame period as that of the fundamental wave component of the signal "a".Additionally, the signals "b" and "c" have respective phases invertedrelative to each other. Consequently, in a region or range in whichnoise having positive polarity relative to the reference voltage V₁ isexpected, the level of the signal "b" is set high for inhibitingdetection of noise of positive polarity. On the other hand, in a regionin which noise having negative polarity relative to the referencevoltage V₁ is expected, the level of the signal "c" is lowered so thatthe noise component of negative polarity is excluded from detection.

Thus, in the receiver shown in FIG. 5, erroneous detection due tofluctuation of the detection output level can be prevented with a highratio or high reliability, to say in another way, whereby the S/N ratioof the received and demodulated signal in the radio transmission cansignificantly and remarkably improved.

FIGS. 7A and 7B show waveforms obtained experimentally for illustratingdifference between the conventional signal detection known heretoforeand the signal detection performed by using the reference signalaccording to the present invention. More specifically, FIG. 7A shows theresult of signal detection where the signal discrimination level is setat a DC level, and FIG. 7B shows the corresponding result obtained withthe receiver implemented in the configuration shown in FIG. 5. In bothcases, signal detection or discrimination based on the positive polarityis shown.

Referring to FIG. 7A, it can be seen that a burst-like signal ofpositive polarity must inherently make appearance at a point "A".However, due to noise and fluctuation, the signal level suffersabnormality, making it impossible to detect the positive burst-likesignal. By contrast, when the same detection output signal is inputtedto the signal discrimination circuit shown in FIG. 5, the referencesignal for the comparator changes, as indicated by the signal "b", inFIG. 6A. Thus, the signal of positive polarity can correctly be detectedeven at a location corresponding to "A" as shown in FIG. 7B.

According to the teachings of the invention, the amplitude (peak-to-peakmagnitude) of the positive reference signal is so set as to fall withina range of 50% to 150% of the amplitude of the normal positiveburst-like signal. By way of example, in the case of the embodimentillustrated in FIG. 7B, the amplitude (peak-to-peak value) of thepositive reference signal is set so as to assume substantially sameamplitude as that of the normal positive burst-like signal. Of course,the amplitude of the negative reference signal is set similarly to thepositive reference signal.

The receiver according to the instant embodiment of the inventiondescribed above can be implemented in a simple structure without needfor using a synchronizing circuit of high accuracy because improvementof the dynamic characteristics of the receiver is accomplished byresorting to analogue technique. Moreover, fluctuation of the signallevel due to various environmental factors in the radio communication,fluctuation of the data clock in the transmission equipment, swing orchanges of phase due to multiple path and other which may provide causesfor minute variation of the clock periodicity can flexibly be copedwith.

FIG. 8 is a block diagram showing a structure of radio receivingequipment according to another embodiment of the present invention. Inthe figure, parts serving for equivalent or same functions as thosedescribed hereinbefore by reference to FIG. 4 are denoted by likereference characters and repeated description thereof is omitted. InFIG. 8, reference numerals 40 and 41 denote correlative demodulatingparts, respectively, for demodulating codes or sequences differingmutually, 42 and 43 denote detecting parts, respectively, 44 and 45denote positive polarity comparators, respectively, and a numeral 46denotes an adder part. In the receiving apparatus shown in FIG. 4, it ispresumed that data for transmission undergo a DPSK modulation by usingspread sequence which remains invariable. By contrast, in the receivingapparatus shown in FIG. 8, it is presumed that the spreading code orsequence is changed in correspondence to the data for transmission, asindicated by PN1 and PN2. Referring to FIG. 8, the signal receivedthrough the medium of antenna is amplified to a prescribed level to besubsequently inputted to the correlative demodulating parts 40 and 41from the received signal input part 9.

The correlative demodulating parts 40 and 41 match or collate thereceived signal with preset spreading codes or sequences. Uponcoincidence between the received signal and one of the spread codes orsequences, a burst-like demodulated signal is outputted from therelevant demodulating part, whereon the demodulated output is detectedby the detecting part 42 or 43. In secession, presence or absence of thesignal is discriminated by the positive polarity comparator 44 or 45,which is then followed by demodulation of the data by the datademodulating part 5. Subsequently, the demodulated data is outputtedfrom the demodulated data output part 10 in timing or synchronism withthe data clock generated by the synchronizing pulse generating part 6.

Since the burst-like demodulated data signal is outputted from eitherone of the correlative demodulating part 40 or 41 in dependence on thedata as received, the outputs of the correlative demodulating parts 40and 41 are added together by the adder part 46, output of which thenundergoes level detection by the level detecting part 7, wherein thesignal 51 as obtained is synthesized or combined by the signalcombination part 27 with a sinusoidal waveform of a same period as thedemodulated burst-like signal extracted from the synchronizing pulsegenerating part 6 via the band limiting part 26, to thereby obtain asignal 52, which is then used as the comparison reference voltage forthe positive polarity comparators 44 and 45, respectively. By virtue ofsuch arrangement as described above, the reference voltage for thepositive polarity comparators 44 and 45, respectively, change incorrespondence to change of the level of the output from the detectingparts 42 and 43 due to variation of the received signal level, as in thecase of the radio receiving apparatus shown in FIG. 4. Thus, a stabledata demodulation can be realized in spite of possible level change orvariation of the received signal due to fluctuation of the radiocommunication environment.

FIGS. 9A and 9B show waveform diagrams for illustrating the signals 50,51, 52 and 53 generated in the radio receiver apparatus shown in FIG. 8.

In the receiver apparatus according to the instant embodiment of theinvention, it is assumed that the spread sequence or code is changed incorrespondence to the data for transmission. It should however beappreciated that similar advantageous effects can equally be obtainedeven in the case where the parameter such as frequency or the like ischanged in place of the spread code or sequence.

Although the foregoing description has been directed to the spectrumspread type receiving apparatus, it should be appreciated that theteachings of the present invention can equally be applied to othersystems designed for processing other type burst-like signals.

Many modifications and variations of the present invention are possiblein the light of the above techniques. It is therefore to be understoodthat within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described.

We claim:
 1. A radio receiver apparatus, comprising:correlativedemodulating means for demodulating correlatively a spread signal;detecting means for detecting a correlation signal demodulated by saidcorrelative demodulating means; level detecting means for detecting alevel of the correlation signal; means for generating a dynamicreference signal for signal discrimination from a level detection signaloutputted from said level detecting means on a basis of the leveldetected; comparing means for comparing a detection signal outputtedfrom said detecting means with said dynamic reference signal; and datademodulating means for demodulating data from a compared signaloutputted from said comparing means.
 2. The radio receiver apparatusaccording to claim 1, further comprising:synchronization pulsegenerating means for generating from the compared signal a synchronizedpulse signal synchronized with the detection signal; means forextracting a signal component of a synchronous frequency from thesynchronized pulse signal; and delay means for delaying an output ofsaid extracting means for a predetermined time period, wherein saidmeans for generating said dynamic reference signal further includesmeans for generating said dynamic reference signal by combining theoutput of said delay means and the detection signal.
 3. The radioreceiver apparatus according to claim 1, said dynamic reference signalgenerating means including:means for generating a first reference signalfor discriminating detection output of positive polarity; and means forgenerating a second reference signal for discriminating detection outputof negative polarity, wherein said comparing means includes:firstcomparing means for comparing the detection output of positive polaritywith said first reference signal; and second comparing means forcomparing the detection output of negative polarity with said secondreference signal.
 4. The radio receiver apparatus according to claim 3,wherein said means for generating said dynamic reference signalincludes:means for generating from the level detection signal said firstreference signal of a same polarity as that of the level detectionsignal; and means for generating said second reference signal byinverting the level detection signal relative to a predeterminedreference signal.
 5. The radio receiver apparatus according to claim 2,said dynamic reference signal generating means including:means forgenerating a first reference signal for discriminating detection outputof positive polarity; and means for generating a second reference signalfor discriminating detection output of negative polarity, wherein saidcomparing means includes:first comparing means for comparing thedetection output of positive polarity with said first reference signal;and second comparing means for comparing the detection output ofnegative polarity with said second reference signal.
 6. The radioreceiver apparatus according to claim 5, wherein said means forgenerating said dynamic reference signal includes:means for generatingsaid first reference signal of a same polarity as that of the leveldetection signal; and means for generating said second reference signalby inverting the level detection signal relative to a predeterminedreference signal.
 7. The radio receiver apparatus according to claim 1,wherein said correlative demodulating means includes a SAW matchedfilter.
 8. A radio receiver apparatus, comprising:correlativedemodulating means for demodulating correlatively signals spread bydifferent modulating signals, said correlative demodulating means beingprovided in accordance with types of said modulating signals,respectively; detecting means for detecting correlation signalsdemodulated by said correlative demodulating means separately from eachother; level detecting means for combining the correlation signals,thereby detecting a level; means for generating a dynamic referencesignal for signal discrimination from a level detection signal outputtedfrom said level detecting means on a basis of the level detected;comparing means for comparing a detection signal outputted from saiddetecting means with said dynamic reference signal; and datademodulating means for demodulating data from a compared signaloutputted from said comparing means.
 9. The radio receiver apparatusaccording to claim 8, further comprising:synchronization pulsegenerating means for generating from the compared signal a synchronizedpulse signal synchronized with the detection signal; means forextracting a signal component of a synchronous frequency from thesynchronized pulse signal; and delay means for delaying an output ofsaid extracting means for a predetermined time period, wherein saidmeans for generating said dynamic reference signal further includesmeans for generating said dynamic reference signal by combining anoutput of said delay means and the level detection signal.
 10. Adiscriminative signal identification method in a spread spectrum typeradio receiver, comprising the steps of:demodulating correlatively aspread signal; detecting a level of a correlation signal demodulated bya correlative demodulating part; generating a first signal for receivedsignal discrimination from a level detection signal obtained in saidstep of detecting the level on a basis of the level detected; extractinga signal component of a synchronous frequency from a receptionsynchronizing clock; generating a second signal synchronized with adetection signal obtained by detecting the correlation signal bydelaying the signal component of the synchronous frequency for apredetermined time period; generating a dynamic reference signal fordiscrimination of a received signal by combining said first and secondsignals; and discriminating the received signal by comparing saiddynamic reference signal with the detection signal.